The in vivo efficacy of peptides is often compromised by their conformational and proteolytic instabilities in addition to their low cellular permeation. Modified peptides have been shown to overcome some or all of these limitations (Moellering et al., Nature 462:182 (2009); Home et al., Proc. Nat'l Acad. Sci. USA 106:14751 (2009)). A synthetic method for stabilizing peptides in the desired helical conformation has been introduced (Patgiri et al., Acc. Chem. Res. 41:1289 (2008); Liu et al., J. Am. Chem. Soc'y 130:4334-37 (2008); Chapman et al., Biochemistry 47:4189-95 (2008)). In this strategy—termed the hydrogen bond surrogate (HBS) approach—a main chain hydrogen bond is replaced with a covalent bond to stabilize the helical conformation, as shown in FIG. 1. HBS α-helices have been shown to target their cognate protein receptors with high affinity and specificity (Patgiri et al., Nat. Chem. Biol. 7:585 (2011); Henchey et al., J. Am. Chem. Soc'y 132:941 (2010); Henchey et al., ChemBioChem 11:2104 (2010); Wang et al., Angew. Chem. Int'l Ed. 47:1879 (2008); Wang et al., Angew. Chem. Int'l Ed. 44:6525 (2005)). The stabilized α-helices can modulate chosen intracellular protein—protein interactions while their unconstrained counterparts remain ineffective (Patgiri et al., Nat. Chem. Biol. 7:585 (2011); Henchey et al., J. Am. Chem. Soc'y 132:941 (2010)).
The proteolytic stability of HBS α-helices composed of α-amino acids was investigated earlier, and it was found that there is a direct correlation between helicity and proteolytic stability, because proteases bind and cleave peptides in the extended conformation (Wang et al., Angew. Chem. Int'l Ed. 44:6525 (2005); Tyndall et al., Chem. Rev. 105:973 (2005)). However, the extent of proteolytic stability of HBS α-helices was found to be sequence dependent.
β-peptides and chimeric α/β-peptides have been known to resist degradation (Hook et al., Chem. Biodivers. 2:591 (2005); Seebach & Gardiner, Acc. Chem. Res. 41:1366 (2008); Home & Gellman, Acc. Chem. Res. 41:1399 (2008); Sadowsky et al., ChemBioChem 8:903 (2007)). Oligomers composed of β3- and mixtures of α- and β3-residues are typically preorganized through side chain-to-side chain contacts (Arvidsson et al., Chem. Commun. 649 (2001); Kritzer et al., J. Am. Chem. Soc'y 127:167 (2005); Hart et al., J. Am. Chem. Soc'y 125:4022 (2003); Cheng & DeGrado, J. Am. Chem. Soc'y 123:5162 (2001)) or use of cyclic amino acid analogs with predefined φ, ψ-dihedral angles (Horne & Gellman, Acc. Chem. Res. 41:1399 (2008); (Appella et al., Nature 387:381 (1997); Vaz et al., ChemBioChem 9:2254 (2008)). It was unknown whether insertion of β3-residues within the macrocycle of HBS helices could lead to more stable HBS helices that also retain their functional properties, nor whether the stability of HBS helices containing attached peptides could be improved by replacing α-amino acid residues in the attached peptide with β3-residues without comprising the functional properties of the HBS helix.
The present invention is directed to overcoming these and other deficiencies in the art.